This invention relates to an irrigation system for use on sloping or uneven terrain, and particularly such a system of the linear or center-pivot type. If of the center-pivot type, one end of the system is pivotally mounted at a central location in the field for rotation of the system about a generally vertical axis at the pivot location. A center-pivot system may irrigate a generally circular area, or a nearly square area with the recent development of the center-pivot corner system as shown and described in U.S. Pat. Nos. 3,802,627 and 3,902,668, the entirety of which are incorporated herein by reference. If of the linear type, neither end is pivotally mounted, but instead both ends move down the field to be irrigated, although the path followed by the system may be either straight or curved.
The center-pivot and linear systems are similar in many respects, both having a relatively large conduit extending over portions of the land or field to be irrigated and which is supported at intervals, such as by self-propelled support towers. The term "self-propelled" in the irrigation art typically refers to a tower having wheels which are driven to move the tower, and thus the conduit supported thereon, over the field. The conduit is usually composed of sections, or spans, which are coupled end-to-end with a support tower for each span. Means are provided for maintaining these spans in alignment, i.e., such that the irrigation conduit appears straight when looking down on the system, as the system moves over the field to be irrigated. The present invention includes either type of system for use on sloping or uneven terrain.
The problems of maintaining alignment and control of the system without excessive tension or compression loads in the spans or at the connections between the spans, and so that the system will follow a true and repeatable path over the field, are considerably greater on sloping or uneven terrain than on flat terrain. To illustrate with a center-pivot type system with one end of the system pivotally mounted, if the system extends downhill from the central pivot location, the system will be in tension. If it extends uphill, it will be in compression. Also, as one or more of the support towers along the length of the system moves over uneven terrain so that it moves up and down hills or in and out of draws as it traverses the field, tension and compression loads are created in the system. If the slope or unevenness of the terrain is relatively severe, these loads can be excessive causing control problems and even damage to the system. These problems can be even more severe with a linear system where neither end is pivotally mounted, but instead both ends must move down the field. Controlling and guiding a linear system is inherently more difficult, so that the problems of sloping or uneven terrain become even more acute.
The present invention solves the problems associated with sloping or uneven terrain in providing an irrigation system with means for sensing tension and compression forces in the system caused by sloping or uneven terrain, and with means for controlling the movement of one or more support towers in response to sensing such a load for relieving the load in the system. In a preferred embodiment of the invention, the sensing means includes at least one coupling for connecting adjacent conduit sections of the system, the coupling having a pivotal yoke arrangement to which the ends of the adjacent conduit sections are connected, and wherein the yoke is pivotally displaced in response to such a load. The preferred embodiment also includes one or more support towers having steerable wheels and wherein the wheels of one or more of the towers are steered in response to the pivotal displacement of the yoke to effect a corrective movement of the tower to relieve the load.
The invention will now be described in more detail with reference to the drawings, but first the drawings themselves will be briefly described.